In recent years, there has been an increasing demand for a clean energy because global warming has been predicted to occur due to the greenhouse effect caused by an increase of CO2. While a nuclear power generation does not discharge CO2, a method for processing the radioactive waste has not been established yet. For this reason, there is a demand for a clean energy with a higher level of safety. Among such expected clean energies, a solar cell particularly has high expectations because of its cleanness, safeness, and manageability.
A general solar cell has a photoelectric conversion part formed of a multilayer structure including a pn junction or a pin junction, which is formed by using: a crystalline semiconductor material, such as single-crystalline silicon and polycrystalline silicon; an amorphous semiconductor material typified by amorphous silicon; or a compound semiconductor material, such as GaAs and CuInSe. The solar cell is configured so that an electron-hole pair is generated in the photoelectric conversion part by incidence of light, and is then taken out to the outside via a pair of electrodes.
The solar cell is generally provided with a concave and convex profile, called a textured surface, on a light receiving surface of the photoelectric conversion part. Incident light beams are scattered by the concave and convex profile, so that the optical path length of each light beam incident in the photoelectric conversion part is increased. In this way, the photoelectric conversion efficiency is improved.
In addition, for the purpose of improving the photoelectric conversion efficiency and the weather resistance, Japanese Patent Application Publication No. Hei 5-335610 describes a technique in which a protective film containing particles on a light receiving surface is formed. Japanese Patent Application Publication No. Hei 5-335610 achieves an increase in photoelectric conversion efficiency by scattering light beans incident on the solar cell by using the particles in the protective film so as to increase the optical path length of each light beam in the photoelectric conversion part.
However, even when the protective film described in Japanese Patent Application Publication No. Hei 5-335610 is used in a solar cell provided with a textured surface in the light receiving surface, a sufficient photoelectric conversion efficiency has not been able to be obtained.
In view of the above-described problems, an object of the present invention is to provide a solar cell and a solar cell module each capable of obtaining a sufficient photoelectric conversion efficiency.